In the process of limiting the speed of the opening or closing of a door, the prior art generally addresses damping situations of rotating doors with a rotary-type damper, which is used in order to prevent a door to be closed abruptly by controlling its rotating force (U.S. Pat. No. 2,047,468, WO/2009/091132 and WO/2010/044567). For rotary doors applications, the prior art also provides a damper used to gradually close a door by employing high polymer viscous liquid and a return spring, wherein the door is automatically closed by the accumulated recovering force of the spring while a braking force is generated by the resistance of the high viscous liquid (CA 2,040,333). The prior art also addresses the control of motion of a door in one direction only by the resistance of viscous liquid (CA 2,015,449).
The damping of sliding doors may also be triggered by an evaluation and control unit, which determines the braking moment by evaluating a momentary door movement, detected by a sensory mechanism, and activates a damper of the doors in order to remain below a predefined maximum velocity (WO/2006/072318). The damping of a sliding door has also been addressed by the prior art by mounting a brake on the sliding door, therefore braking the closing motion of the sliding door by activating an oil damper (WO/2009/081827). The damping of a sliding door may also be achieved by a speed regulator managing the speed of a closing door (U.S. Pat. No. 6,633,094). Door damping has also been demonstrated by cylinders containing oil and pistons. When the door opens, oil is drawn into a cylinder. When the door closes, the oil is expulsed from the cylinder through an orifice, therefore controlling the closing speed of the door (U.S. Pat. No. 5,291,630).
Other existing sliding door systems are based on air-type damping cylinders for the function of damping the movement of the door equipment at the end of stroke.
Sliding doors are often found on railcars, buses, airplanes, mining equipment, cars, and other types of vehicles, as well as in various stationary applications in all sorts of properties (e.g. residential, industrial, or commercial settings). A general problem that is often present on equipment provided with sliding doors arises when a sliding door is moving rapidly. This problem may occur in various circumstances, for example, but not limited to, while a vehicle is in motion or when an excessive force is applied to open or close a sliding door. Most sliding doors are currently suspended on friction-free rollers. A friction-free roller is an element that allows a sliding door to slide freely. In the particular example of a moving vehicle, if a sliding door panel is unlatched and free to slide while the vehicle is changing speed, the resulting movement of the unlatched door panel will be in a direction opposite to that of the vehicle, thereby causing the door panel to accelerate until the end of stroke.
This undesired door motion creates both a safety hazard and a mechanical hazard. The safety hazard occurs, for example, when a heavy door accelerates and rams into people, animals or objects, while the mechanical hazard occurs when a heavy door accelerates and rams into an end-of-travel device thereof. Hence, during heavy acceleration or deceleration of a vehicle, unlatched sliding doors will move and accelerate in a direction opposite to that of the vehicle. An unlatched sliding door thus poses an increased risk of violently hitting a passenger, an animal, an object or the end-of-travel device thereof, thereby possibly injuring beings or damaging itself and its surroundings in the process.
In view of the above considerations, there is therefore a need for a roller system that is able to act as a damper when a door panel speed increases and to impose an increasing braking force thereon while remaining friction-free at low speeds.